Stretching Micro Metal Particles into Uniformly Dispersed and Sized Nanoparticles in Polymer

Abstract

There is a longstanding challenge to disperse metal nanoparticles uniformly in bulk polymers for widespread applications. Conventional scale-down techniques often are only able to shrink larger elements (such as microparticles and microfibers) into micro/nano-elements (i.e. nanoparticles and nanofibers) without much altering their relative spatial and size distributions. Here we show an unusual phenomenon that tin (Sn) microparticles with both poor size distribution and spatial dispersion were stretched into uniformly dispersed and sized Sn nanoparticles in polyethersulfone (PES) through a stack and draw technique in thermal drawing. It is believed that the capillary instability plays a crucial role during thermal drawing. This novel, inexpensive, and scalable method overcomes the longstanding challenge to produce bulk polymer-metal nanocomposites (PMNCs) with a uniform dispersion of metallic nano-elements.

Figure 1

PES-5 Sn composite preform fabrication with poor metal distribution. (a) Schematic of the thermal consolidation process. (b) A typical optical microscope image from the longitudinal cross-section of a PES-5 Sn composite perform (scale bar: 40 μm). (c) Sn microparticles size distribution in a PES-5 Sn composite perform.

Figure 2

PES-5Sn nanocomposites by thermal drawing. (a) Schematic of the thermal drawing process. (b) Schematic of the stack and draw iteration. (c) SEM image of the longitudinal cross-section of PES-5Sn nanocomposite fiber with an inset to show high magnification (scale bar: 2 μm, inset: 500 nm). (d) Sn nanoparticle size distribution in PES-5Sn nanocomposites fiber (after the third cycle of the thermal drawing). (e) TEM image of Sn nanoparticles when PES cladding is dissolved after the third cycle of thermal drawing (scale bar: 50 nm). (f) Atomic resolution TEM image of Sn twinned-nanoparticles with polygonal shapes showing many facets as confirmed by their ring patterns (insets) (see Supplemental Table 2 for indexed diffraction patterns) (scale bar: 2 nm).

Figure 3

Metal droplet deformation during thermal drawing. (a) Evolution of metal droplet/wire during cyclic thermal drawing. (b) SEM image of the composite fiber longitudinal cross-section after several consecutive cuts were made on the fiber surface (after first thermal drawing cycle) (scale bar: 50 μm). (c) SEM images of a thin film cut from the PES-5Sn nanocomposite fiber (after the third cycle of the thermal drawing) with an inset to show high magnification (scale bar: 5 μm, inset: 1 μm).

Figure 4

Binarized images and Index of Dispersion processed by ImageJ for spatial distribution analysis. (a) A typical optical microscope image from a longitudinal cross-section of the initial composite preform processed by ImageJ software (scale bar is 100 μm). (b) A typical SEM image of the longitudinal cross-section of the PES-5Sn nanocomposite fiber processed by ImageJ software (scale bar is 300 nm).